Description: Purpose: Fibroblast growth factor receptor 1 ( FGFR1 ) and FGFR2 amplifications are observed in approximately 10% of breast cancers and are related to poor outcomes. We evaluated whether dovitinib (TKI258), an inhibitor of FGFR1, FGFR2, and FGFR3, presented antitumor activity in FGFR -amplified breast cancers. Experimental Design: Preclinical activity of dovitinib was evaluated in both breast cancer cell lines and an FGFR1 -amplified xenograft model (HBCx2). Dovitinib was then evaluated in a phase II trial that included 4 groups of patients with human EGF receptor 2–negative metastatic breast cancer on the basis of FGFR1 amplification and hormone receptor (HR) status. FGFR1 amplification was assessed by silver in situ hybridization. Preplanned retrospective analyses assessed predictive value of FGFR1 , FGFR2 , and FGF3 amplifications by quantitative PCR (qPCR). Results: Dovitinib monotherapy inhibits proliferation in FGFR1 - and FGFR2 -amplified, but not FGFR -normal, breast cancer cell lines. Dovitinib also inhibits tumor growth in FGFR1 -amplified breast cancer xenografts. Eighty-one patients were enrolled in the trial. Unconfirmed response or stable disease for more than 6 months was observed in 5 (25%) and 1 (3%) patient(s) with FGFR1 -amplified/HR-positive and FGFR1 -nonamplified/HR-positive breast cancer. When qPCR-identified amplifications in FGFR1 , FGFR2 , or FGF3 were grouped to define an FGF pathway–amplified breast cancer in HR-positive patients, the mean reduction in target lesions was 21.1% compared with a 12.0% increase in patients who did not present with FGF pathway–amplified breast cancer. Conclusion: Dovitinib showed antitumor activity in FGFR -amplified breast cancer cell lines and may have activity in breast cancers with FGF pathway amplification. Clin Cancer Res; 19(13); 3693–702. ©2013 AACR .